Iraqi Shi'ite militia fighters say they have driven Islamic State extremists from an air base to the west of Mosul, threatening the supply route from Syria for extremist militants in the northern Iraqi city.

Yusif al-Kallabi, a spokesman for a coalition of mostly Iranian-backed Shi'ite militias called the Popular Mobilization Units, told Iraqi state TV on November 16 that the air base at the town of Tal Afar had been "liberated."

If confirmed, the capture of the base would be a significant development in the campaign to recapture Mosul, the last major stronghold for IS militants in Iraq.

Tal Afar is about 60 kilometers west of Mosul on the main highway to Syria.

Iraqi government forces, police, and allied Sunni tribesman have advanced to the southern and northern outskirts of Mosul itself, backed by Kurdish Peshmerga fighters to the north and northeast.

Meanwhile, Iraqi special forces are engaged in urban combat within the city's easternmost district.

But IS militants have still had a logistical supply line to the west of Mosul stretching into Syria.

Hadi al-Amiri, leader of the Badr Organization, the largest force in the Popular Mobilization militia coalition, said on November 16 that the capture of Tal Afar will be "the starting block for the liberation of all the area to the Syrian border and beyond" into Syria.

Turkey has armored columns poised on its border with northern Iraq within the Turkish district of Silopi.

In between Silopi and Tal Afar is territory still controlled by IS fighters that includes a section of a major oil pipeline that links the Taq Taq oil field in Iraq's Kurdish autonomous region to an eastern Mediterranean port near the Turkish city of Ceyhan.

Although Iraq's Kurdistan region had been exporting oil to Turkey through that pipeline for years, it has been inoperable since February 2016, when IS militants cut it off by capturing territory near Iraq's borders with Syria and Turkey across from the Turkish town of Silopi.